Pixel circuit for organic light emitting display and driving method thereof, organic light emitting display

ABSTRACT

A pixel circuit for an organic light emitting display includes first, second, third, fourth, fifth, and sixth MOS transistors, a first capacitor, and an organic light emitting diode. During a initialization stage, the sixth MOS transistor is turned on, and a reference voltage is transmitted to the gate electrode of the second MOS transistor. During a data-writing stage, the first MOS transistor is turned on and a data signal is transmitted to the first terminal of the first capacitor, the fourth MOS transistor is turned on and the other MOS transistors are turned off. During a light emitting stage, the fifth MOS transistor is turned on and the voltage at the gate of the second MOS transistor is based on the data signal. As a result, the third MOS transistor generates a drive current based on the data signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese patent application No.201210577002.8 titled “PIXEL CIRCUIT FOR ORGANIC LIGHT EMITTING DISPLAYAND DRIVING METHOD THEREOF, ORGANIC LIGHT EMITTING DISPLAY” and filedwith State Intellectual Property Office of PRC on Dec. 26, 2012, whichis incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to organic light emitting displays, andmore particularly to a pixel circuit for an organic light emittingdisplay, a driving method thereof, and the organic light emittingdisplay.

BACKGROUND OF THE INVENTION

With the continuous development of multimedia devices, the organic lightemitting diode (OLED) has been increasingly used in high performancedisplays. In order to be adapted to large display size, a shorterdriving time for a single pixel is required for a traditional passivematrix OLED. Therefore, an increased transient current is needed,resulting in increased power consumption. At the same time, the use oflarge current may lead to a too large voltage drop in a pixel array, sothat the operation voltage of the OLED is too high and the powerefficiency is reduced. However, in the active matrix organic lightemitting diode (AMOLED), the problems are well solved by progressivelyscanning input OLED current line by line.

In AMOLED devices, pixel circuits formed with polysilicon thin filmtransistors are usually used to provide current for the OLED device.Compared with amorphous silicon thin film transistors, polysilicon thinfilm transistors have higher mobility and more stable characteristics.Accordingly, they are more suitable for AMOLED displays. However, due tothe limitation of the crystallization process, the polysilicon thin filmtransistors made on a large glass substrate usually have heterogeneityin electrical parameters such as threshold voltage and mobility, and theheterogeneity may lead to differences in the current and brightness ofthe OLED display device.

In addition, in the application of large size displays, due to theresistance of the power line for the backplane and the fact that drivecurrent for all the pixel units is supplied by the same power line, thesupply voltage in a region closer to the power supply is higher thanthat in regions farther from the power supply in the backplane. Thisphenomenon is called IR Drop.

Given the correlation of the current with the supply voltage, the IRDrop may also cause current differences in different regions, andaccordingly the OLED display devices in different regions have differentbrightness.

In the related art, a variety of technical solutions are utilized tosolve the problem of brightness differences in the OLED display devices.For example, a South Korea patent application No. 1020100102872disclosed a pixel compensation circuit. However, there are still manyproblems in the existing technical solutions, such as a large number ofsignal lines and complex peripheral drive circuits.

BRIEF SUMMARY OF THE INVENTION

One inventive aspect is a pixel circuit for an organic light emittingdisplay. The pixel circuit includes an organic light emitting diode, afirst MOS transistor, including a gate electrode, a first electrode, anda second electrode, and a second MOS transistor, including a gateelectrode, a first electrode, and a second electrode. The firstelectrode of the second MOS transistor is coupled to a first powersupply. The pixel circuit also includes a third MOS transistor,including a gate electrode, a first electrode, and a second electrode,where the first electrode of the third MOS transistor is coupled to thesecond electrode of the second MOS transistor, and the second electrodeof the third MOS transistor is coupled to a second power supply via theorganic light emitting diode. The pixel circuit also includes a fourthMOS transistor, including a gate electrode, a first electrode, and asecond electrode, where the first electrode of the fourth MOS transistoris coupled to the gate electrode of the second MOS transistor, and thesecond electrode of the fourth MOS transistor is coupled to the secondelectrode of the second MOS transistor. The pixel circuit also includesa fifth MOS transistor, including a gate electrode, a first electrode,and a second electrode, a sixth MOS transistor, including a gateelectrode, a first electrode, and a second electrode, where the secondelectrode of the sixth MOS transistor is coupled to the gate electrodeof the second MOS transistor. The pixel circuit also includes a firstcapacitor, including first and second terminals, where the firstterminal of the first capacitor is coupled to the second electrode ofthe first MOS transistor and is coupled to the second electrode of thefifth MOS transistor, and the second terminal is coupled to the gateelectrode of the second MOS transistor and is coupled to the firstelectrode of the fourth MOS transistor. The gate electrode of the first

MOS transistor receives a first scanning signal, the first electrode ofthe first MOS transistor receives a data signal, the gate electrode ofthe third MOS transistor receives a control signal, the gate electrodeof the fourth MOS transistor receives the first scanning signal, thegate electrode of the fifth MOS transistor receives the control signal,the first electrode of the fifth MOS transistor receives a referencevoltage, the gate electrode of the sixth MOS transistor receives asecond scanning signal, and the first electrode of the sixth MOStransistor receives the reference voltage.

Another inventive aspect is a driving method for a pixel circuit. Thepixel circuit includes an organic light emitting diode, a first MOStransistor, including a gate electrode, a first electrode, and a secondelectrode, and a second MOS transistor, including a gate electrode, afirst electrode, and a second electrode. The first electrode of thesecond MOS transistor is coupled to a first power supply. The pixelcircuit also includes a third MOS transistor, including a gateelectrode, a first electrode, and a second electrode, where the firstelectrode of the third MOS transistor is coupled to the second electrodeof the second MOS transistor, and the second electrode of the third MOStransistor is coupled to a second power supply via the organic lightemitting diode. The pixel circuit also includes a fourth MOS transistor,including a gate electrode, a first electrode, and a second electrode,where the first electrode of the fourth MOS transistor is coupled to thegate electrode of the second MOS transistor, and the second electrode ofthe fourth MOS transistor is coupled to the second electrode of thesecond MOS transistor. The pixel circuit also includes a fifth MOStransistor, including a gate electrode, a first electrode, and a secondelectrode, a sixth MOS transistor, including a gate electrode, a firstelectrode, and a second electrode, where the second electrode of thesixth MOS transistor is coupled to the gate electrode of the second MOStransistor. The pixel circuit also includes a first capacitor, includingfirst and second terminals, where the first terminal of the firstcapacitor is coupled to the second electrode of the first MOS transistorand is coupled to the second electrode of the fifth MOS transistor, andthe second terminal is coupled to the gate electrode of the second MOStransistor and is coupled to the first electrode of the fourth MOStransistor. The method includes during an initialization stage, turningoff the first MOS transistor and the fourth MOS transistor via the firstscanning signal, turning off the third MOS transistor and the fifth MOStransistor via the control signal, and turning on the sixth MOStransistor via the second scanning signal, where the reference voltageis transmitted to the gate electrode of the second MOS transistorthrough the sixth MOS transistor.

Another inventive aspect is an organic light emitting display includinga scanning drive unit, a data drive unit, N scan lines, M data lines,and a plurality of pixel circuits. Each of the pixel circuits includesan organic light emitting diode, a first MOS transistor, including agate electrode, a first electrode, and a second electrode, and a secondMOS transistor, including a gate electrode, a first electrode, and asecond electrode. The first electrode of the second MOS transistor iscoupled to a first power supply. Each pixel circuit also includes athird MOS transistor, including a gate electrode, a first electrode, anda second electrode, where the first electrode of the third MOStransistor is coupled to the second electrode of the second MOStransistor, and the second electrode of the third MOS transistor iscoupled to a second power supply via the organic light emitting diode.Each pixel circuit also includes a fourth MOS transistor, including agate electrode, a first electrode, and a second electrode, where thefirst electrode of the fourth MOS transistor is coupled to the gateelectrode of the second MOS transistor, and the second electrode of thefourth MOS transistor is coupled to the second electrode of the secondMOS transistor. Each pixel circuit also includes a fifth MOS transistor,including a gate electrode, a first electrode, and a second electrode, asixth MOS transistor, including a gate electrode, a first electrode, anda second electrode, where the second electrode of the sixth MOStransistor is coupled to the gate electrode of the second MOStransistor. Each pixel circuit also includes a first capacitor,including first and second terminals, where the first terminal of thefirst capacitor is coupled to the second electrode of the first MOStransistor and is coupled to the second electrode of the fifth MOStransistor, and the second terminal is coupled to the gate electrode ofthe second MOS transistor and is coupled to the first electrode of thefourth MOS transistor. The gate electrode of the first MOS transistorreceives a first scanning signal, the first electrode of the first MOStransistor receives a data signal, the gate electrode of the third MOStransistor receives a control signal, the gate electrode of the fourthMOS transistor receives the first scanning signal, the gate electrode ofthe fifth MOS transistor receives the control signal, the firstelectrode of the fifth MOS transistor receives a reference voltage, thegate electrode of the sixth MOS transistor receives a second scanningsignal, and the first electrode of the sixth MOS transistor receives thereference voltage. The scanning drive unit is configured to providescanning signals to respective scan lines, the data drive unit isconfigured to provide data signals to respective data lines, and theplurality of the pixel circuits are respectively arranged in pixel areasformed near intersections of the scan lines and the data lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a pixel circuit according to anembodiment in the prior art;

FIG. 2 is a timing diagram of driving signals for the pixel circuitshown in FIG. 1;

FIG. 3 is a schematic diagram of a pixel circuit according to anembodiment of the present invention;

FIG. 4 is a timing diagram of driving signals for the pixel circuitshown in FIG. 3; and

FIG. 5 is a schematic structural diagram of an organic light emittingdisplay according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Particular embodiments of the invention are illustrated herein inconjunction with the drawings.

Various details are set forth herein as they relate to certainembodiments. However, the invention can also be implemented in otherways different from the ways described herein, and modifications can bemade by those skilled in the art without departing from the invention.Therefore, the invention is not limited to particular embodimentsdisclosed hereinafter.

As described above, AMOLED display devices have the problem of unevenbrightness due to the influence of the threshold voltages of thepolysilicon thin film transistors and the IR drop on the power line forthe backplane. In order to solve these problems, a voltage driven pixelcircuit including five polysilicon thin film transistors and onecapacitor (5T1C) is usually used in the prior art. As shown in FIG. 1,the pixel circuit of the prior art includes a first PMOS transistor MP1,a second PMOS transistor MP2, a third PMOS transistor MP3, a fourth PMOStransistor MP4, a fifth PMOS transistor MP5, a capacitor Cth and anorganic light emitting diode D1.

The gate electrode of the first PMOS transistor MP1 receives a scanningsignal scan2, the source electrode of the first PMOS transistor MP1receives a data signal Vdata, and the drain electrode of the first PMOStransistor MP1 is connected to the first terminal n1 of the capacitorCth. The second terminal n2 of the capacitor Cth is connected to thegate electrode of the second PMOS transistor MP2. The source electrodeof the second PMOS transistor MP2 receives a first power supply VDD, andthe drain electrode of the second PMOS transistor MP2 is connected tothe source electrode of the third PMOS transistor MP3. The gateelectrode of the third PMOS transistor MP3 receives a control signal“emit”, and the drain electrode of the third PMOS transistor MP3 isconnected to the anode of the organic light emitting diode D1. Thecathode of the organic light emitting diode 1 is connected to a secondpower supply VEE. The gate electrode of the fourth PMOS transistor MP4receives a scanning signal scan1, the source electrode of the fourthPMOS transistor MP4 is connected to the second terminal n2 of thecapacitor Cth, and the drain electrode of the fourth PMOS transistor MP4is connected to the drain electrode of the second PMOS transistor MP2.The gate electrode of the fifth PMOS transistor MP5 receives the controlsignal “emit”, the source electrode of the fifth PMOS transistor MP5receives a reference voltage Vref, and the drain electrode of the fifthPMOS transistor MP5 is connected to the first terminal n1 of thecapacitor Cth.

FIG. 2 shows a timing diagram of driving signals for the pixel circuitin FIG. 1. The operational principle of the pixel circuit shown in FIG.1 is described in further detail in conjunction with the FIG. 2 asfollows.

In Stage t1, both the scanning signal scanl and the control signal“emit” are at a low level. Therefore, the second PMOS transistor MP2,the third PMOS transistor MP3, the fourth PMOS transistor MP4 and thefifth PMOS transistor MP5 are turned on. In this Stage, the secondterminal n2 of the capacitor Cth is pulled down to a low potential, andthe first terminal n1 of the capacitor Cth is applied with voltage Vref.

In Stage t2, the control signal “emit” is turned into high level, andthe third PMOS transistor MP3 and the fifth PMOS transistor MP5 areturned off In addition, the scanning signal scanl is turned to a lowlevel. Because the scanning signal scanl and the scanning signal scan2are in the low level, the first PMOS transistor MP1 and the fourth PMOStransistor MP4 are on. In this case, the first terminal n1 of thecapacitor Cth is connected to the data signal Vdata, and a voltage(VDD−Vth) based on the threshold voltage Vth of the second PMOStransistor MP2 is developed at the second terminal n2 of the capacitorCth. The voltage difference across the capacitor Cth is Vdata−(VDD−Vth).

In Stage t3, the scanning signal scan1 is turned to high level, and thefourth PMOS transistor MP4 is turned off.

In Stage t4, the control signal “emit” is turned to low level.Accordingly, the third PMOS transistor MP3 and the fifth PMOS transistorMP5 are turned on. In this case, the voltage at the first terminal n1 ofthe capacitor Cth becomes Vref. According to the law of chargeconservation, the voltage at the second terminal n2 of the capacitor Cthbecomes Vref−Vdata+(VDD−Vth), and the second PMOS transistor MP2 isturned on or off according to the voltage at the second terminal n2.

The voltage difference between the source electrode and the gateelectrode of the second PMOS transistor MP2 isVsg=VDD−Vref+Vdata−(VDD−Vth)=Vdata-−ref+Vth. It can be concluded thatthe current flowing through the second PMOS transistor MP2 isIm2=k(Vdata−Vref)̂2, where k is a constant coefficient which is relatedto the mobility, the width to length ratio and the gate-sourcecapacitance value of the MOS transistor. Thus the compensation for thethreshold voltage Vth and the first supply voltage VDD is achieved.

However, in the pixel circuit described above, there is an overlapbetween the scanning signal scan1 and the scanning signal scan2 in timesequence. Specifically, referring to FIG. 2, both the scanning signalscanl and the scanning signal scan2 are in low level in Stage t2. Thestructure and operation of the peripheral drive circuit for the pixelcircuit with such structure is, therefore, complicated.

In addition, in the pixel circuit described above, it is necessary tocontinuously provide the data signal Vdata with a high potential to thedrain electrode of the first PMOS transistor MP1. That is to say, thedata line connected to the first PMOS transistor MP1 can not be leftfloating, otherwise the compensation for the threshold voltage Vth andthe first supply voltage VDD can not be achieved in this circuit. Thisis because the drain electrode of the first PMOS transistor MP1 isconnected to the drain electrode of the fifth PMOS transistor MP5. InStage t1, when the fifth PMOS transistor MP5 is turned on, the voltageat the drain electrode of the fifth PMOS transistor MP5 is Vref. If thedata line is left floating, a leakage current may occur in the drainelectrode of the first PMOS transistor MP1, leading to an unstablevoltage at the first terminal n1 of the capacitor Cth. Hence, thevoltage difference across the capacitor Cth may change, and thus thecompensation for the threshold voltage and the first supply voltage cannot be actually achieved. Moreover, the need to continuously provide thedata signal with high potential increases both the difficulty in ICdevelopment and the power consumption of the circuit.

The present invention provides a pixel circuit for an organic lightemitting display, whereby the waveform of each driving signal can bedefined to simplify the structure of the drive circuit and the powerconsumption of the circuit can be reduced. Specifically, FIG. 3 shows aschematic circuit diagram of a pixel circuit for an organic lightemitting display according to an embodiment of the present invention.

As shown in FIG. 3, the pixel circuit according to the embodiment of thepresent invention includes a first MOS transistor M1, a second MOStransistor M2, a third MOS transistor M3, a fourth MOS transistor M4, afifth MOS transistor M5, a sixth MOS transistor M6, a first capacitor C1and an organic light emitting diode D1.

The gate electrode of the first MOS transistor M1 receives a firstscanning signal S1, the first electrode of the first MOS transistor M1receives a data signal VDATA, and the second electrode of the first MOStransistor M1 is connected to the first terminal N1 of the firstcapacitor C1. The second terminal N2 of the first capacitor C1 isconnected to the gate electrode of the second MOS transistor M2. Thefirst electrode of the second MOS transistor M2 is connected to a firstpower supply VDD, and the second electrode of the second MOS transistorM2 is connected to the first electrode of the third MOS transistor M3.The gate electrode of the third MOS transistor M3 receives a controlsignal EMIT, and the second electrode of the third MOS transistor M3 iscoupled to a second power supply VEE via the organic light emittingdiode D1. The first electrode of the fourth MOS transistor M4 isconnected to the second terminal N2 of the first capacitor C1, thesecond electrode of the fourth MOS transistor M4 is connected to thesecond electrode of the second MOS transistor M2, and the gate electrodeof the fourth MOS transistor M4 receives the first scanning signal S1.The gate electrode of the fifth MOS transistor M5 receives the controlsignal EMIT, the first electrode of the fifth MOS transistor M5 receivesa reference voltage VREF, and the second electrode of the fifth MOStransistor M5 is connected to the first terminal N1 of the firstcapacitor C1. The gate electrode of the sixth MOS transistor M6 receivesa second scanning signal S2, the first electrode of the sixth MOStransistor M6 receives the reference voltage VREF, and the secondelectrode of the sixth MOS transistor M6 is connected to the gateelectrode of the second MOS transistor M2.

Specifically, in this embodiment, the first MOS transistor, the secondMOS transistor, the third MOS transistor, the fourth MOS transistor, thefifth MOS transistor and the sixth MOS transistor are all PMOStransistors. The first electrode refers to the source electrode of eachof the PMOS transistors. The second electrode refers to the drainelectrode of each of the PMOS transistors.

It should be noted that in other embodiments, the first MOS transistor,the second MOS transistor, the third MOS transistor, the fourth MOStransistor, the fifth MOS transistor and the sixth MOS transistor mayalso be NMOS transistors. Of course, the invention is not limitedthereto, and other variations can be made in the first MOS transistor tothe sixth MOS transistor by those skilled in the art. For example, oneor more of the transistors may be PMOS transistors, and one or moreother transistors may be NMOS transistors.

FIG. 4 shows a timing diagram of the scanning signals and the controlsignal for the pixel circuit according to the present invention. Theoperational principle of the pixel circuit according to the presentinvention will be described in further detail in conjunction with theFIG. 3 and the FIG. 4 below.

Referring to the FIG. 4, in Stage T1, both the first scanning signal S1and the control signal EMIT are in high level. Accordingly, the firstMOS transistor M1, the third MOS transistor M3, the fourth MOStransistor M4 and the fifth MOS transistor M5 are turned offFurthermore, the second scanning signal S2 is in low level and the sixthMOS transistor M6 is turned on. The reference voltage VREF istransmitted to the gate electrode of the second MOS transistor M2through the sixth MOS transistor M6, and the voltage at the secondterminal N2 of the first capacitor C1 is VREF.

In Stage T2, the first scanning signal S1 is turned to low level, andthus the first MOS transistor M1 is turned on. In response, the voltageat the first terminal N1 of the first capacitor C1 becomes VDATA.Furthermore, the fourth MOS transistor M4 is turned on, so that a diodeconnection is formed in the second MOS transistor M2. In this case, thevoltage at the second terminal N2 of the first capacitor C1 is VDD−Vth(Vth is the threshold voltage of the MOS transistor), and thus thevoltage difference across the first capacitor C1 is VDATA−(VDD−Vth).Moreover, the second scanning signal S2 is turned to high level, andthus the sixth MOS transistor M6 is turned off. The control signal EMITis still high level, and thus the third MOS transistor M3 and the fifthMOS transistor M5 are turned off

In Stage T3, the first scanning signal S1 is turned to high level, andthus the first MOS transistor M1 and the fourth MOS transistor M4 areturned off. The second scanning signal S2 is in high level, and thus thesixth MOS transistor M6 is turned off. The control signal EMIT is turnedto low level, and thus the third MOS transistor M3 and the fifth MOStransistor M5 are turned on. The voltage at the first terminal N1 of thefirst capacitor C1 is reset because the fifth MOS transistor M5 isturned on. Accordingly, the voltage at the first terminal N1 of thefirst capacitor C1 is VREF. According to the law of charge conservation,the voltage at the second terminal N2 of the first capacitor C1 isVREF−VDATA+(VDD−Vth). Accordingly, the voltage difference between thesource electrode and the gate electrode of the second MOS transistor M2is Vsg=VDD−VREF+VDATA−(VDD−Vth)=VDATA−VREF+Vth. It can be concluded thatthe current flowing through the second MOS transistor M2 isIm2=k(Vdata−Vref)̂2, where k is a constant coefficient which is relatedto the mobility, the width to length ratio and the gate-sourcecapacitance value of the MOS transistor. The organic light emittingdiode D1 is driven to emit light when the third MOS transistor M3 isturned on.

It can be known from the above mentioned operational principle that thecompensation for the threshold voltage Vth and the first supply voltageVDD has been achieved through the pixel circuit according to theembodiment of the present invention. Moreover, it can be seen from theFIG. 4 that the first scanning signal S1 and the second scanning signalS2 are independent of each other in time sequence and are not bothturned on at the same time. Accordingly, a more simple drive circuit canbe used to provide the drive signals, and the operation of the drivecircuit is more convenient. In addition, since the drive signals areindependent of each other in the time sequence, the multi-channelselection of the pixel circuit can be achieved so as to improve theintegrity and convenience of the pixel circuit.

In addition, according to the embodiment of the present invention, in aninitialization stage (i.e. Stage T1), it is not necessary tocontinuously provide the data signal VDATA to the pixel circuit. This isbecause the fourth MOS transistor M4 is not turned on in theinitialization stage, so there is no resistance drop by the second PMOStransistor MP2 and the third PMOS transistor MP3 as shown in FIG. 1, butthe second terminal N2 of the first capacitor C1 is charged to thepotential VREF directly. Meanwhile, neither the first MOS transistor M1nor the fifth MOS transistor M5 is turned on. Therefore the leakagecurrent does not occur at the first terminal N1 of the first capacitorC1. Accordingly, the data line connected to the first MOS transistor M1can be left floating. The pixel circuit with this structure reduces thedifficulty in IC development and power consumption of the circuit, sinceit is not necessary to continuously provide the data signal VDATA with arelatively high potential.

The present invention further provides a driving method for the pixelcircuit shown in FIG. 3. The driving method includes the followingstages. In an initialization stage, the first MOS transistor M1 and thefourth MOS transistor M4 are turned off via the first scanning signalS1, the third MOS transistor M3 and the fifth MOS transistor M5 areturned off via the control signal EMIT, the sixth MOS transistor M6 isturned on via the second scanning signal S2, and the reference voltageVREF is transmitted to the gate electrode of the second MOS transistorM2 through the sixth MOS transistor M6.

In a data-writing stage, the first MOS transistor M1 and the fourth MOStransistor M4 are turned on via the first scanning signal S1, and thedata signal VDATA is transmitted to the first terminal of the firstcapacitor C1 through the first MOS transistor M1, and the fourth MOStransistor M4 is turned on, resulting in a diode connection formed inthe second MOS transistor M2; the sixth MOS transistor M6 is turned offvia the second scanning signal S2, and the third MOS transistor M3 andthe fifth MOS transistor M5 are turned off via the control signal EMIT.

In a light emitting stage, the first MOS transistor M1 and the fourthMOS transistor M4 are turned off via the first scanning signal S1, thesixth MOS transistor M6 is turned off via the second scanning signal S2,the fifth MOS transistor M5 and the third MOS transistor M3 are turnedon via the control signal EMIT. The voltage across the first capacitorC1 is reset due to the turning on of the fifth MOS transistor M5, acorresponding drive current is generated by the third MOS transistor M3based on the reset of the voltage across the first capacitor C1, and thedrive current is configured to drive the organic light emitting diode D1to emit light.

The data signal may be provided in the data-writing stage, while thedata signal may be not provided in the initialization stage and thelight emitting stage. In other words, the data line can be left floatingin the initialization stage and the light emitting stage.

The present invention further provides an organic light emittingdisplay. As shown in FIG. 5, the organic light emitting displayincludes: a scanning drive unit 10, a data drive unit 20, N scan lines(S1, S2, . . . , Sn), M data lines (D1, D2, . . . , Dm) and multiplepixel circuits (P11, P12, . . . , P1m, P21, P22, . . . , P2m, . . . ,Pn1, Pn2, . . . , Pnm). The structures of the pixel circuits are similarto that of the pixel circuit shown in FIG. 3.

Specifically, the scanning drive unit 10 is configured to providescanning signals to respective scan lines (S1, S2, . . . , Sn). The datadrive unit 20 is configured to provide data signals to respective datalines (D1, D2, . . . , Dm). The multiple pixel circuits are respectivelyarranged in pixel areas formed by intersection of the N scan lines andthe M data lines.

In each of the pixel circuits for the organic light emitting displayaccording to the present invention, the gate electrodes of the first MOStransistor M1 and the fourth MOS transistor M4 may be both connected tothe nth scan line, and the gate electrode of the sixth MOS transistor M6is connected to the (n+1)th scan line, where 1<n<N.

In other embodiments, the gate electrode of the first MOS transistor M1,the gate electrode of the fourth MOS transistor M4 and the gateelectrode of the sixth MOS transistor M6 may be connected to the scanlines in other ways, which are not limited to the embodiment describedabove.

Compared with the drive circuit in the prior art, the scanning drivecircuit for the organic light emitting display according to theembodiment of the present invention is simpler in structure and moreconvenient in operation for employing the pixel circuit shown in FIG. 3.In addition, it is not necessary to continuously provide the data signalto the data line in the initialization stage. Therefore, the powerconsumption of the organic light emitting display according to theembodiment of the present invention is also lower than that in the priorart.

Though the present invention is disclosed by way of specific embodimentsas described above, those embodiments are not intended to limit thepresent invention. Based on the methods and the technical aspectsdisclosed above, possible variations and changes may be made to thetechnical solutions of the present invention by those skilled in the artwithout departing from the spirit and the scope of the presentinvention. Therefore, any change, equivalent alternation, ormodification made to the above embodiments according to the principle ofthe present invention, which do not depart from the subject matters ofthe present invention, fall within the scope of protection of thepresent invention.

What is claimed is:
 1. A pixel circuit for an organic light emittingdisplay, the pixel circuit comprising: an organic light emitting diode;a first MOS transistor, comprising a gate electrode, a first electrode,and a second electrode; a second MOS transistor, comprising a gateelectrode, a first electrode, and a second electrode, wherein the firstelectrode of the second MOS transistor is coupled to a first powersupply; a third MOS transistor, comprising a gate electrode, a firstelectrode, and a second electrode, wherein the first electrode of thethird MOS transistor is coupled to the second electrode of the secondMOS transistor, and the second electrode of the third MOS transistor iscoupled to a second power supply via the organic light emitting diode; afourth MOS transistor, comprising a gate electrode, a first electrode,and a second electrode, wherein the first electrode of the fourth MOStransistor is coupled to the gate electrode of the second MOStransistor, and the second electrode of the fourth MOS transistor iscoupled to the second electrode of the second MOS transistor; a fifthMOS transistor, comprising a gate electrode, a first electrode, and asecond electrode; a sixth MOS transistor, comprising a gate electrode, afirst electrode, and a second electrode, wherein the second electrode ofthe sixth MOS transistor is coupled to the gate electrode of the secondMOS transistor; and a first capacitor, comprising first and secondterminals, wherein the first terminal of the first capacitor is coupledto the second electrode of the first MOS transistor and is coupled tothe second electrode of the fifth MOS transistor, and the secondterminal is coupled to the gate electrode of the second MOS transistorand is coupled to the first electrode of the fourth MOS transistor,wherein the gate electrode of the first MOS transistor receives a firstscanning signal, the first electrode of the first MOS transistorreceives a data signal, the gate electrode of the third MOS transistorreceives a control signal, the gate electrode of the fourth MOStransistor receives the first scanning signal, the gate electrode of thefifth MOS transistor receives the control signal, the first electrode ofthe fifth MOS transistor receives a reference voltage, the gateelectrode of the sixth MOS transistor receives a second scanning signal,and the first electrode of the sixth MOS transistor receives thereference voltage.
 2. The pixel circuit according to claim 1, whereinthe first scanning signal and the second scanning signal do not overlap.3. The pixel circuit according to claim 1, wherein the first MOStransistor, the second MOS transistor, the third MOS transistor, thefourth MOS transistor, the fifth MOS transistor and the sixth MOStransistor are PMOS transistors.
 4. The pixel circuit according to claim1, wherein the first MOS transistor, the second MOS transistor, thethird MOS transistor, the fourth MOS transistor, the fifth MOStransistor and the sixth MOS transistor are NMOS transistors.
 5. Adriving method for a pixel circuit, the pixel circuit comprising: anorganic light emitting diode; a first MOS transistor, comprising a gateelectrode, a first electrode, and a second electrode; a second MOStransistor, comprising a gate electrode, a first electrode, and a secondelectrode, wherein the first electrode of the second MOS transistor iscoupled to a first power supply; a third MOS transistor, comprising agate electrode, a first electrode, and a second electrode, wherein thefirst electrode of the third MOS transistor is coupled to the secondelectrode of the second MOS transistor, and the second electrode of thethird MOS transistor is coupled to a second power supply via the organiclight emitting diode; a fourth MOS transistor, comprising a gateelectrode, a first electrode, and a second electrode, wherein the firstelectrode of the fourth MOS transistor is coupled to the gate electrodeof the second MOS transistor, and the second electrode of the fourth MOStransistor is coupled to the second electrode of the second MOStransistor; a fifth MOS transistor, comprising a gate electrode, a firstelectrode, and a second electrode; a sixth MOS transistor, comprising agate electrode, a first electrode, and a second electrode, wherein thesecond electrode of the sixth MOS transistor is coupled to the gateelectrode of the second MOS transistor; and a first capacitor,comprising first and second terminals, wherein the first terminal of thefirst capacitor is coupled to the second electrode of the first MOStransistor and is coupled to the second electrode of the fifth MOStransistor, and the second terminal is coupled to the gate electrode ofthe second MOS transistor and is coupled to the first electrode of thefourth MOS transistor, wherein the gate electrode of the first MOStransistor receives a first scanning signal, the first electrode of thefirst MOS transistor receives a data signal, the gate electrode of thethird MOS transistor receives a control signal, the gate electrode ofthe fourth MOS transistor receives the first scanning signal, the gateelectrode of the fifth MOS transistor receives the control signal, thefirst electrode of the fifth MOS transistor receives a referencevoltage, the gate electrode of the sixth MOS transistor receives asecond scanning signal, and the first electrode of the sixth MOStransistor receives the reference voltage, wherein the method comprises:during an initialization stage, turning off the first MOS transistor andthe fourth MOS transistor via the first scanning signal, turning off thethird MOS transistor and the fifth MOS transistor via the controlsignal, and turning on the sixth MOS transistor via the second scanningsignal, wherein the reference voltage is transmitted to the gateelectrode of the second MOS transistor through the sixth MOS transistor.6. The driving method according to claim 5, further comprising during adata-writing stage, turning on the first MOS transistor and the fourthMOS transistor via the first scanning signal, wherein the data signal istransmitted to the first terminal of the first capacitor through thefirst MOS transistor, and the second MOS transistor is diode coupled bythe fourth MOS transistor, turning off the sixth MOS transistor via thesecond scanning signal, and turning off the third MOS transistor and thefifth MOS transistor via the control signal.
 7. The driving methodaccording to claim 6, further comprising during a light emitting stage,turning off the first MOS transistor and the fourth MOS transistor viathe first scanning signal, turning off the sixth MOS transistor via thesecond scanning signal, turning on the fifth MOS transistor and thethird MOS transistor via the control signal, wherein a voltage at thegate electrode of the second MOS transistor is based on the data signal,a drive current is generated by the third MOS transistor based on thedata signal, and the drive current is configured to cause the organiclight emitting diode to emit light according to the data signal.
 8. Thedriving method according to claim 5, wherein the data signal is providedduring the data-writing stage and the data signal is not provided duringthe initialization stage and during the light emitting stage.
 9. Thedriving method according to claim 5, wherein the first scanning signaland the second scanning signal do not overlap.
 10. An organic lightemitting display comprising: a scanning drive unit; a data drive unit; Nscan lines; M data lines; and a plurality of pixel circuits, each of thepixel circuits comprising: an organic light emitting diode; a first MOStransistor, comprising a gate electrode, a first electrode, and a secondelectrode; a second MOS transistor, comprising a gate electrode, a firstelectrode, and a second electrode, wherein the first electrode of thesecond MOS transistor is coupled to a first power supply; a third MOStransistor, comprising a gate electrode, a first electrode, and a secondelectrode, wherein the first electrode of the third MOS transistor iscoupled to the second electrode of the second MOS transistor, and thesecond electrode of the third MOS transistor is coupled to a secondpower supply via the organic light emitting diode; a fourth MOStransistor, comprising a gate electrode, a first electrode, and a secondelectrode, wherein the first electrode of the fourth MOS transistor iscoupled to the gate electrode of the second MOS transistor, and thesecond electrode of the fourth MOS transistor is coupled to the secondelectrode of the second MOS transistor; a fifth MOS transistor,comprising a gate electrode, a first electrode, and a second electrode;a sixth MOS transistor, comprising a gate electrode, a first electrode,and a second electrode, wherein the second electrode of the sixth MOStransistor is coupled to the gate electrode of the second MOStransistor; and a first capacitor, comprising first and secondterminals, wherein the first terminal of the first capacitor is coupledto the second electrode of the first MOS transistor and is coupled tothe second electrode of the fifth MOS transistor, and the secondterminal is coupled to the gate electrode of the second MOS transistorand is coupled to the first electrode of the fourth MOS transistor,wherein the gate electrode of the first MOS transistor receives a firstscanning signal, the first electrode of the first MOS transistorreceives a data signal, the gate electrode of the third MOS transistorreceives a control signal, the gate electrode of the fourth MOStransistor receives the first scanning signal, the gate electrode of thefifth MOS transistor receives the control signal, the first electrode ofthe fifth MOS transistor receives a reference voltage, the gateelectrode of the sixth MOS transistor receives a second scanning signal,and the first electrode of the sixth MOS transistor receives thereference voltage, wherein the scanning drive unit is configured toprovide scanning signals to respective scan lines, the data drive unitis configured to provide data signals to respective data lines, and theplurality of the pixel circuits are respectively arranged in pixel areasformed near intersections of the scan lines and the data lines.
 11. Theorganic light emitting display according to claim 10, wherein the gateelectrodes of the first MOS transistor and the fourth MOS transistor areboth coupled to an nth scan line, and the gate electrode of the sixthMOS transistor is coupled to an (n+1)th scan line, where 1<n<N.
 12. Theorganic light emitting display according to claim 10, wherein the firstscanning signal and the second scanning signal do not overlap.
 13. Theorganic light emitting display according to claim 10, wherein the firstMOS transistor, the second MOS transistor, the third MOS transistor, thefourth MOS transistor, the fifth MOS transistor and the sixth MOStransistor are PMOS transistors.
 14. The organic light emitting displayaccording to claim 10, wherein the first MOS transistor, the second MOStransistor, the third MOS transistor, the fourth MOS transistor, thefifth MOS transistor and the sixth MOS transistor are NMOS transistors.